As compound semiconductor luminescent devices including a GaN layer, such as blue LEDs have been widely utilized, compound semiconductor luminescent devices having a larger luminescence output have been required.
In a conventional compound semiconductor luminescent device, a compound semiconductor function layer including a GaN layer is provided on a growth substrate made of electricity-insulating sapphire, and two electrodes are provided on the compound semiconductor function layer. In the case of the conventional compound semiconductor luminescent device, two light-opaque electrodes provided on a luminescent surface obstructs luminescent light, thereby lowering the luminescence output, wherein the luminescent surface is the one of the two surfaces of the compound semiconductor function layer, that is opposite to the sapphire growth substrate.
Therefore, a compound semiconductor luminescent device has been proposed (for example, see Patent Reference 1) which has a structure consisting of an electroconductive substrate (thermal expansion coefficient of 16.2×10−6/° C.) consisting of Cu, a compound semiconductor function layer including a GaN layer, and an electrode that are stacked in this order. With such a structure, another electrode can be provided on the opposite surface to the one of the electroconductive substrate on which the compound semiconductor function layer is provided, or the electroconductive substrate can play the role of the another electrode; therefore, only a single electrode can be provided on the luminescent surface.
EP-1385215 A2 (Patent Reference 2) describes a method of producing a nitride semiconductor device having at least one or more p-type nitride semiconductor layers, an active layer with a quantum well structure including at least a well layer made of AlaInbGa1−a−bN (0≦a≦1, 0≦b≦1, a+b≦1) and a barrier layer made of AlcIndGa1−c−dN (0≦c≦1, 0≦d≦1, c+d≦1), and one or more n-type nitride semiconductor layers on one principal surface of a substrate having two opposing principal surfaces, the method comprising growing at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on one principal surface of a growth substrate having two opposing principal surfaces and having a thermal expansion coefficient larger than those of the above-described n-type and p-type nitride semiconductor layers to form a bonding laminate, and providing a first bonding layer made of one or more metal layers on the above-described p-type nitride semiconductor layer, while providing a second bonding layer made of one or more metal layers on one principal surface of a substrate having two opposing principal surfaces and having a thermal expansion coefficient that is larger than those of the above-described n-type and p-type nitride semiconductor layers and the same as or smaller than that of the above-described growth substrate; causing the first bonding layer and the second bonding layer to oppose each other to bond the bonding laminate with the above-described substrate by heat pressure welding; and removing the growth substrate of the above-described bonding laminate. However further higher luminescence output has been required, i.e., a compound semiconductor luminescent device has been required that employs an electroconductive substrate made of a metal, includes a GaN layer, and has a further higher luminescence output.    [Patent Reference 1] JP-A-2004-47704    [Patent Reference 2] EP 1385215 A2